The present invention relates to a multi-layer elastic flat-shaped article, formed from at least two outer layers comprising a porous fiber material, such as polyolefin fiber batting, and at least one middle layer, which consists of adhesive skeins applied in linear fashion.
German Patent DE-AS 28 35 822, entitled xe2x80x9cAbsorptive Laminate and Procedurexe2x80x9d, relates to a laminate structure that consists of two absorbent layers formed from cellulose fibers, and a middle layer. The middle layer is an adhesive divided into dots or strip shapes, which can also be formed from intersecting lines. However, this patent does not disclose a multi-layer flat-shaped article that results in an air-permeable, highly elastic sheet, using fusion adhesives.
In the adhesive skein configuration according to FIG. 2 of German Patent DE-AS 28 35 822, care is taken to ensure that the adhesive distribution does not interrupt air permeability. As a result, the adhesive is provided, such that a highly elastic middle layer is produced, which gives elasticity to the flat shaped article, so that the fiber materials that form the outer layers can be easily distorted, but by themselves remain inelastic.
U.S. Pat. No. 5,342,469, expressly incorporated herein by reference, relates to a method for making a composite with a discontinuous adhesive structure.
U.S. Pat. No. 4,606,964, expressly incorporated herein by reference, relates to a bulked web composite article, and method for the manufacture thereof.
U.S. Pat. No. 5,514,470, expressly incorporated herein by reference, relates to a composite plastic-bonded material.
See also, U.S. Pat. Nos. 5,835,881, 5,789,065, 5,462,708, 5,283,733, 5,178,931, 4,801,482, and 5,159,706, expressly incorporated herein by reference.
In order to provide a multi layer laminate structure, having an air-permeable, highly elastic sheet, using fusion adhesives, the present invention uses adhesive skeins of a thermoplastic material that is elastic at room temperature. The configuration of the adhesive skeins forms a latticework which permits elastic stretching under tensile loading, and restoration of the adhesive skein configuration when tension is released.
According to the present invention, the adhesive skeins can be advantageously applied by means of a printing process. For this, normal printing processes are suitable, such as intaglio printing, flexoprinting, or screen printing. The adhesive skeins are applied in lattice fashion on one, or on both, layers of material to be laminated. Here, for example, a heated intaglio printer can be used, whose intaglio cylinder is engraved in such a way that a lattice-shaped, waffle-like application results on the batting material strip. The same holds true for the flexoprinting or screen printing processes. After the lattice-shaped application, the strips are placed adjacent to one on another and glued using the thermoplastic adhesive.
Materials suitable as batting substances are well known in the art. For example, materials which can be manufactured employing a plaiting strip and can be formed using the spun batten process or the melt-blown process. Thus, the thickness of the batten can vary greatly, according to the manufacturing process and parameters thereof. It is also possible to have the applied adhesive skein penetrate at least partially into the batting material, thus achieving improved attachment. According to the present invention, special value is placed on the configuration of the adhesive skeins. These can be applied in parallel, as straight or meandering strips. However, preferably they will be adhesive skeins which run into each other (intersect) in specular zig-zag or sinusoid curves that will overlap or touch at their vertices, so that a waffle-like configuration results.
It is also possible to regularly interrupt the adhesive skeins using a valve-controlled nozzle, so that relatively short segments are always produced; these likewise ensure that the flat-shaped article will be elastic. The interruptions may be regularly spaced or randomly or pseudorandomly spaced, such as by the inclusion of bubbled within the heated adhesive. However, the interruptions are preferably not coincident across the laminated structure, unless a frangible, weak, or irreversibly stretched location is desired.
Additionally, the invention relates to a procedure for manufacturing a multi-layer elastic flat-shaped article, which consists of at least two outer layers made of a porous fiber material and of at least one rubbery elastic middle layer.
A process according to the present invention is characterized in that, by means of a printing process or pressing out of skein, adhesive skeins which consist of a thermoplast that is elastic at room temperature, are applied to a substrate made of porous fiber material. The configuration of the adhesive skeins produces a two-dimensional latticework. Under tensile loading and relieving, elastic stretching and recovery of the adhesive skein configuration is permitted.
The adhesive can be applied using multiple nozzles, so that strands are formed perpendicular to a direction of movement of the material strips to be laminated. A waffle-shaped or lattice-type application, or a rectangular structure, can result from nozzles that move correspondingly opposite each other.
According to another aspect of the invention, it is possible to provide an adhesive thickness greater in the edge area of a flat-shaped article than in the middle area. The resulting flat-shaped article can be processed to form panty liners or sanitary napkins or similar items. Such a structure may also be useful to fabricate disposable diapers.
In each case, it is an aspect of the present invention that the adhesives employed which remain elastic at room temperature and can be processed as hot-setting adhesives. By elastic, it is meant that the material, in its applied configuration, will allow the composite structure, including two laminated layers, to be stretched without delamination of the skein from both layers or tension-related failure of the adhesive. The minimum tolerable degree of stretch may vary for differing applications will vary, for example, from 1% up to near the tensile elongation limit of the batting material. Often, however, it is desired that the batting not be subjected to destructive elongation. Therefore, the elongation of the laminate may advantageously be limited by a non-linear increase in tension as the adhesive is stretched. For example, as the skein pattern is stretched, the elements of the pattern become straightened. When they are almost fully straightened, the forces resisting elongation shift from the forces of the batting supporting the skein in its non-linear normal state to the elastic forces of the skein and laminated layers together. As the tension further increases, a further non-linear increase in tension may occur due to an inherent non-linear elongation-force relationship of either the adhesive, layers, or both. While preferably the skein does not delaminate from the layers during normal use, the product may be designed to selectively delaminate to provide desired elongation properties or as a preferred failure mode. If the elastic retains a tacky surface, it may, after elongation and partial delamination, re-adhere to the layers.
It should also be understood that, while the invention described below relates to production of a three layer laminate, greater number of layers may be adhered to achieve desired properties. It is also understood that the materials and configuration for each layer may differ. Thus, the laminate need not be reversible nor symmetric.
These and other objects will become apparent. For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.